...I make it. It depends on the curve of that side. That's assuming that your drawing of the brace actually includes the thickness of the front panel, as it appears to. I just calculated the area if the sides were straight and then added a little bit. And I didn't add any to make up for the volume of the brace.

The best way is to place your internal brace on a sheet of large graph paper, draw around it and count the squares. Divide the desired volume in cubic inches ((3660 in3) by the area of the brace (102 in2) to get the height in inches (35.9").